It’s essentially a guarantee that certain tools and system APIs will be available, accept certain arguments, and accept/return data formatted in a specific way. It’s important for general purpose software and portability. Basically, if you want your software to run on anything and everything, you target POSIX. Except Windows, obviously, but pretty much everything else is POSIX compatible, or close enough that you’re probably fine.
An example: I write medical applications that are distributed to many hospitals, so well outside of my direct control. One program in particular is run on Windows, Linux, or AIX. I have to write separate handling for Windows obviously, but all I need to do to support both Linux and AIX is stick to POSIX APIs and test on Linux. Which is great, because I don’t have access to an AIX system. I still have to do final testing on AIX, but with one minor exception in the last five years, it all just works.
It’s the only piece of consumer software I’ve ever used that I straight-up thought should be illegal after I tried it. If you’re a parent, and you’re wondering if you should let your child explore Roblox: DON’T. Ban any videos that mention Roblox from their apps, do not install the game, and do not ever give that company a single cent. The entire structure is designed to torment children and yank on their psychological levers until they beg their parents to buy them in-game currency to turn their low-low into a high-high for a couple of minutes, then restart the cycle.
There are VIP areas that you have to have a subscription (pay) to go into, and devs are incentivized to add them by kickbacks, so they show up in just about every game. In competitive games where you chase other players to catch them, if you don’t have VIP the other players can literally just go through a wall you can’t pass to get away. Then they can get boosts in the VIP area to get an unfair advantage.
There’s the “revenge” buttons, where if someone in a competitive game wins against you, it gives you a button you can click to to punish the other player in various ways. Naturally, it costs real money.
Obstacle courses start out decent, but once you’re far enough in that the sunk cost fallacy is in effect, it ramps the difficulty up massively and frustrates you over and over. And each time you respawn it makes you walk past the item you can buy that will make this frustrating part disappear and get you back to the nice dopamine hits like you had earlier in the map.
And of course, every game tries to make people who buy the pay-to-win items as visible as possible, and make it look as spectacular as possible. It’s masterful psychological manipulation, and while the games with these exploitative systems are made by devs external to Roblox itself, the economy and reward systems that shaped those games is defined by Roblox. It’s actually worse that you have external devs, because it insulates Roblox from the responsibility for these exploitative mechanics, while Roblox acts as the bank you use to buy currency for the games. Roblox only cares about money, and they don’t care how many abusive things their games have to do to kids to get it.
I’m about as far from a pearl-clutcher as you can get while still being a responsible parent, but even before considering that the social features are repeatedly being used to groom children, Roblox simply should not be allowed to exist. Play Goat Simulator 3 with your kid instead. Or Minecraft. Or Terraria. A Lego game. Bayonetta. I don’t care–anything but Roblox.